The closest prior art known to the applicants is European Patent No. 0 014 983. This European patent is directed to a method for the preparation of dialkylmagnesium compounds R.sub.2 Mg, wherein R is alkyl, by the reaction of magnesium hydride MgH.sub.2 or magnesium and hydrogen with an olefin in the presence of a catalyst. The gist of the process is the nature of the catalyst. Thus, the catalyst may either be
(a) magnesium organic compounds together with halides of a transition metal of sub-groups IV to VIII of the Periodic System, or PA1 (b) magnesium hydride together with halides of sub-groups IV to VIII of the Periodic System. The magnesium hydride or catalyst (b), in turn, has been prepared from magnesium and hydrogen (1 to 300 bar) in the presence of a polycyclic aromatic compound and, optionally, a tertiary amine as activators at temperatures of 0.degree. to 200.degree. C.
Pursuant to this prior art disclosure, the reaction is carried out preferably in the presence of a solvent, tetrahydrofuran being the preferred solvent. The patent teaches that the preferred reaction conditions are pressures of 1 to 300 bar and temperatures of 0.degree. to 200.degree. C.
The preparation of the catalyst as identified above is disclosed and described in the examples of the European patent 0 014 983. Corresponding to these examples, magnesium powder (50 mesh) is first suspended in tetrahydrofuran. Ethyl bromide is added to the suspension and after stirring for half an hour, anthracen is added. The mixture is continually agitated until formation of the magnesium anthracen has taken place. Subsequently, the halide, e.g., chloride, of sub-groups IV through VIII of the Periodic System or Table is added to the mixture. Examples of such chlorides are CrCl.sub.3, TiCl.sub.4, NiCl.sub.2, VCl.sub.4, ZrCl.sub.4 and HfCl.sub.4. After further stirring, the desired colored catalyst solution is formed, the color being dependent on the nature of the halide.
Pursuant to the teaching of this European Patent 0 014 983, this catalyst solution is admixed with magnesium hydride. This results in a suspension and the olefin is now added to this suspension. The addition reaction of the olefin takes place in a temperature range of 0.degree. to 200.degree. C. and at a pressure of 1 to 300 bar.